Geothermal source sections cover systems consist of both shallow and deep geothermal source section. Usually, shallow geothermal boreholes, 15-200 m, are used as heat source for ground source heat pump (GSHP) systems. Deep geothermal boreholes, typically 1-10 km, can retrieve heat with higher temperature, and are used as a heat source for running a geothermal power plant.
In general, the ground temperature is higher than the atmospheric temperature in the winter time. Therefore, a ground source heat pump (GSHP) system absorbs geothermal heat from the ground and uses it for heating. In the summer time, inversely, the atmosphere is cooled in the ground having lower temperature than the atmospheric temperature.
For the vertical closed loop geothermal system which is most widely used among the GSHP systems, various types of grouting materials and grouting methods are known to install a thermal heat exchange system in a borehole which is dug vertically in the ground and to fill up the space between the geothermal heat exchange system and the borehole.
For example, Korean Patent Publication No. 10-0985854 (published on Oct. 8, 2010) discloses a grouting method in which a borehole is formed at a depth of 150 to 200 m in the ground and a vertical closed loop geothermal system is installed, then pebbles having an average diameter of about 5 to 30 mm are charged from the bottom of the borehole to the rock formation to improve the heat conductivity, and grouting is carried out from the rock formation to the ground with non-shrink mortar to prevent the infiltration of external contaminants from flowing into the borehole.
Meanwhile, Korean Patent Publication No. 10-1358251 (published on Feb. 5, 2014) discloses a grouting method in which sticks are inserted into a borehole, where a geothermal heat exchange system is installed, the sticks are being made by filling a long tube that is breakable by expansion with a mixture of 20 to 30% by weight of bentonite and 70 to 80% by weight of silica sand, then the bentonite included in the mixture expands by water to tightly grout the borehole.
In addition, Korean Patent Publication Laid-Open No. 10-2015-0032677 (published on Mar. 27, 2015) discloses a grouting method in which, instead of conventional bentonite grouting material, the crushed rocks are filled up to a natural water level detected in a borehole in which a geothermal heat exchange system is installed at a depth of 150 to 200 m in the ground, and the remaining part is filled with bentonite to prevent the infiltration of external contaminants and to increase the thermal conductivity of the geothermal heat exchange system further.